The technology to which the invention is directed relates to a sealer used for asphalt substrates, such as a sealer for asphalt of the type employed extensively throughout the United States. Pavement technology has developed a series of asphalt coating compositions. Many of the asphalt compositions have been applied to asphalt, sometimes as a protective coating and sometimes as a re-cover system. Such asphalt mixtures have little or no reflectivity in that they are typically black in color, are not solar reflective, do not reduce surface temperatures, and do not reduce pollutants.
However, it has been found that conventional dark pavements rapidly increase in temperature when exposed to sunlight because they absorb 80-95% of the sunlight and significantly contribute to the creation of heat islands. Heat islands are built up areas that are hotter than nearby rural areas. For example, the annual mean air temperature of a city with one million people or more can be 1.8-5.4° F. (1-3° C.) warmer than its surroundings. In the evening, the difference can be as high as 22° F. (12° C.). Heat islands can affect communities by increasing summertime peak energy demand, air conditioning costs, air pollution and greenhouse gas emissions, heat-related illness and mortality, and water quality. According to Akbari et al. hot pavements aggravate urban heat islands by warming the local air, and contribute to global warming by radiating heat into the atmosphere as pavements can aggravate urban heat islands because they comprise about one third of urban surfaces (Akbari H, Rose L S, Taha H. 1999. Characterizing the fabric of the urban environment: A case study of Sacramento, Calif. Lawrence Berkeley National Laboratory). Moreover, hot pavement can also raise the temperature of storm water runoff, which can cause additional negative impacts. Thus there exists a real need for lowering asphalt surface temperatures.
In addition, vehicles traveling on asphalt surfaces have been known to produce significant levels of pollutants. While pollutants have long been known to have a negative environmental impact, photocatalytic air cleaning has also been shown to remove polutants including nitrogen oxides (NOx) and volatile organic compounds (VOCs) from polluted urban air, and, consequently, for reducing concentrations of toxic and irritating ozone, a key constituent of smog that forms on hot, sunny days.
Thus, there is a need for novel high-performance asphalt-based sealcoat compositions that are highly solar reflective, reduce surface temperatures, and reduce pollutants via photocatalytic reactions.